The present invention relates to a metal-made seamless pipe and a process for producing such a pipe. More particularly, the present invention relates to a metal-made seamless pipe which is low in processability but can be produced having a small thickness and a small inner diameter, having superior mechanical strength and gastightness, and which can be suitably used, as a sealing member of a translucent vessel (e.g. a ceramic-made translucent vessel) of, for example, a high-pressure discharge lamp (e.g. a metal halide lamp). The present invention also relates to a process for producing such a metal-made seamless pipe.
As shown in FIG. 5, a translucent ceramic pipe 20 (a translucent pipe) is used as a translucent vessel of a high-pressure discharge lamp 10 (e.g. a metal halide lamp), because the translucent vessel contains a light emitting material (e.g. dysprosium iodide) of high corrosivity and accordingly requires corrosion resistance.
In order to seal the translucent ceramic pipe 20 (a translucent pipe) used as a translucent vessel, a metal-made pipe 30 (e.g. a Mo pipe) was proposed as a sealing member (European Patent Publication EP 0982278A1).
The metal (e.g. Mo or W) used in such a metal-made pipe, however, is generally low in processability and there has been a limit in producing the pipe in a small thickness and a small inner diameter.
Since the metal is low in processability and its cutting is difficult, production of a metal-made pipe therefrom has ordinarily been conducted by sintering a metal ingot and subjecting the sintered metal ingot to rolling, drawing or the like to obtain a pipe-shaped material. In such a production process, it has been extremely difficult to obtain a metal-made pipe of small thickness and small diameter.
In view of the above-mentioned problems, the object of the present invention is to provide a metal-made seamless pipe which is low in processability but can be produced having a small thickness and a small inner diameter, having superior mechanical strength and gastightness, and which can be suitably used as a sealing member of a translucent vessel (e.g. a ceramic-made translucent vessel) of, for example, a high-pressure discharge lamp (e.g. a metal halide lamp), and a process for producing such a metal-made seamless pipe.
In order to achieve the above objects, the present invention provides a metal-made seamless pipe and a process for production thereof, both shown below.
A metal-made seamless pipe is provided containing, as a main component, at least one kind of metal selected from the group consisting of metals each having a melting point of 1,600xc2x0 C. or more. The pipe has a porosity of 0.3 to 25%, when the porosity is defined as a ratio of the open pores present at the outer surface of the pipe to the total surface area (100%) of the outer surface of the pipe without through-pores perforating in the thickness direction of the pipe.
According to another embodiment of the present invention, the metals each having a melting point of 1,600xc2x0 C. or more are preferably Mo, W, Re, Ti, Hf and Zr.
According to another embodiment of the metal-made seamless pipe of the present invention, the melting point of each metal is 2,600xc2x0 C. or more. The metals each having a melting point of 2,600xc2x0 C. or more are preferably Mo, W and Re.
Preferably, the metal-made seamless pipe of the present invention has an inner diameter of 0.4 to 3.0 mm and a thickness of 0.05 to 1.0 mm.
According to another embodiment of the present invention, the metal-made seamless pipe further contains, in addition to the metal, at least one kind of oxide selected from the group consisting of Al2O3, Y2O3, Dy2O3, Gd2O3, Ho2O3 and Tm2O3, in an amount of 0.02 to 5% by volume relative to 100% of the total of the metal and the oxide.
The present invention also provides a process for producing a metal-made seamless pipe, comprising the steps of preparing a mixture containing (1) 80 to 98% by weight of a powder of at least one kind of metal selected from the group consisting of metals each having a melting point of 1,600xc2x0 C. or more and (2) a binder in a solvent, and kneading the mixture for 0 to 3 hours to form a kneaded material. Then, the kneaded material is extruded to form a pipe-shaped material. The pipe-shaped material is dried at a temperature in a range of xe2x88x925 to 25xc2x0 C. for 10 hours (shortest) to 48 hours (longest) from the completion of the extrusion, and thereafter dried at a temperature in a range of 30 to 120xc2x0 C. for 0.5 to 8 hours. The dried material is then fired at a lower temperature selected from a temperature between 1,000 to 2,100xc2x0 C. and a temperature lower by 300xc2x0 C. than the melting point of the metal.
According to the above process for producing a metal-made seamless pipe of the present invention, the metals each having a melting point of 1,600xc2x0 C. or more are preferably Mo, W, Re, Ti, Hf and Zr.
According to another embodiment of the present invention, the melting point of each metal is 2,600xc2x0 C. or more. Preferably, the metals each having a melting point of 2,600xc2x0 C. or more are Mo, W and Re.
According to the present invention, the metal-made seamless pipe obtained after firing of the dried pipe-shaped material at a lower one of a temperature selected from a temperature between 1,000 to 2,100xc2x0 C. and a temperature 300xc2x0 C. lower than the melting point of the metal, has an inner diameter of 0.4 to 3.0 mm and a thickness of 0.05 to 1.0 mm.
According to another embodiment of the present invention, a process for producing a metal-made seamless pipe is provided, wherein the preparation of the mixture further includes the step of adding, in addition to the components used, at least one kind of oxide selected from the group consisting of Al2O3, Y2O3, Dy2O3, Gd2O3, Ho2O3 and Tm2O3, in an amount of 0.02 to 5% by volume relative to 100% of the total of the metal and the oxide.
According to the present invention, the drying of the pipe-shaped material is preferably conducted in an atmosphere containing the vapor of the solvent.